Photovoltaic cells are widely used in residential structures and roofing materials for generation of electricity. A plurality of photovoltaic cells are interconnected in series or in parallel and are integrated with residential structures such as roofing slates, roofing tiles, building claddings and the like. Interest in thin-film photovoltaics has expanded in recent years. This is due primarily to improvements in conversion efficiency of cells made at the laboratory scale, and the anticipation that manufacturing costs can be significantly reduced compared to the older and more expensive crystalline and polycrystalline silicon technology. The term “thin-film” typically refers to the thickness of the photovoltaic p-n junction layers and is used to distinguish this type of solar cell from the more common silicon based cell, which uses a relatively thick silicon wafer. For example, CIGS or CdTe are classes of “thin film” photovoltaic structures (usually less than 10 microns in total thickness). Although these photovoltaic structures can be deposited onto thick, heavy stainless steel or even onto glass, solar cells fabricated in this manner are still considered “thin film” solar cells. In operation, a number of thin-film solar cells are electrically connected to each other and mounted in a support structure or frame called a photovoltaic module. The module is enclosed within a protective panel.
Various transparent encapsulants, such as organic polymers, are used for encapsulating the photovoltaic cell to prevent the incursion of moisture into the photovoltaic cell. A copolymer of ethylene and vinyl acetate (ethylene vinyl acetate (EVA)) is a commonly used polymeric material for encapsulating the photovoltaic cells.
Mechanical tests such as the commonly referred to “peel test” are currently used to quantify the strengths of film stacks that form solar cells. The test parameters employed in these test protocols do not simulate the actual operating conditions of the solar cells and therefore do not yield sufficiently accurate information regarding the solar cells' true behavior over its expected commercial operational lifetime.